A simple nature of charge-transfer (CT) in the prototype complexes D-p - F-2 (D-p = NH3, H2O) manifests itself in a very close shape of their CT excitation energy curves omega(CT)(R) along the donor-acceptor separation R. It affords a simple orbital description in terms of the CT orbitals (CTOs) obtained with a transformation of the virtual orbitals of the standard local density approximation (LDA). The transferable energy of the relevant CTO as a function of R closely approximates the common shape of omega(CT)(R), while the height of the individual curve is determined with the ionization potential of D-p. (C) 2017 Elsevier B.V. All rights reserved.